Various musical instruments exist which use a resonant skin to produce sound waves characteristic to the individual instrument. Examples of such instruments are various percussion instruments and banjos.
A resonant skin comprises a skin which may be organic or synthetic. The skin is attached to a ring, which may be e.g. a metal ring.
The musical instruments comprise a shell with an end edge. The resonant skin is placed on the shell with the skin abutting the end edge. The ring is configured with a size to enclose the shell. The pitch produced by the resonant skin is dependent on how tightly the skin is tensioned. The tensioning of the skin can be adjusted by displacing the ring parallel to a centre axis through the shell, so that the skin is pressed with more or less force against the end edge, tensioning the skin to a larger or smaller degree. The tighter the tensioning, the higher the pitch.
The degree to which the skin must be tensioned to achieve a given pitch is dependent on several different parameters, for instance room temperature, air pressure and air humidity. Therefore, the distance of ring displacement relative to the shell to achieve a given pitch may vary.
For tensioning the skin, a tension adjustment hoop is used, which is placed on top of the resonant skin, so that the resonant skin is between the shell and the tension adjustment hoop. The tension adjustment hoop is connected to tensioning means, which may be attached to the shell, and which may be adjustable, so that the tension adjustment hoop is displaceable relative to the shell for tensioning the resonant skin. On a drum or a banjo, the tensioning means will be evenly distributed around the periphery of the shell to ensure even tensioning.
A musician tunes the instrument by adjusting the pitch before the musician starts playing. During play, it may be necessary to make several minor adjustments. The time consumption for tuning the instrument is largely dependent on the number of tensioning means, whereas the number of tensioning means in turn influences the sound quality produced by the instrument. A compromise is consequently made between the amount of time available to the musician for tuning the instrument during e.g. a concert and the desired sound quality.
Commonly known resonant skins consist of a synthetic skin provided with a welded-on ring, forming a dolly when tensioning the skin. The ring is designed to be flexible relative to its planeness to enable fine-tuning of the resonant skin. When tensioning and commencing use of a new resonant skin, the ring of the skin may be deformed relative to its original shape. During this process, crunching sounds will typically be emitted from the welding. When using the commonly known tuning method, the planeness or deformation of the ring is of minor importance, as the tensioning means are adjusted individually by hand until the desired note is achieved. However, this tuning method is cumbersome and time-consuming. Therefore, previous attempts have been made to invent mechanically and hydraulically acting systems to alleviate this process.
The problems relating to the prior systems are, to a large extent, caused by the fact that their power transfer means, which abuts the ring of the resonant skin, is provided as a coherent circular ring 30 (FIG. 8A), embodied as a tension adjustment hoop, ring or tube. This embodiment of the pressure means would not be able to transfer a sufficient, evenly distributed torque to the ring of the resonant skin 15 (FIG. 8A).
For instance, WO 95/28698 A1 (Martin) 1995-10-26 describes a circular tube located under a tension adjustment hoop. For instance, WO 2007/144706 A2 (CASTAGNA), describes a frame in which a rigid circular ring is pressed against the resonant skin from the inner side. For instance, U.S. Pat. No. 1,054,009 Feb. 25, 1913 (William F. Ludwig) describes different variations of examples 1 and 2.
These examples have the problematic common feature that the power transfer to the ring of the resonant skin is a coherent circular force F (see FIG. 8A).